A conventional treatment apparatus used in a process for manufacturing semiconductor devices is known from, for example, Japanese Patent Application KOKAI Publication No. 63-24615. At the time of subjecting objects to be treated, such as semiconductor wafers (hereinafter referred to simply as "wafers"), to a predetermined treatment, a plurality of wafers are transferred from a cassette as a first support member to a wafer boat as a second support member by means of transfer means, thereby performing the predetermined treatment.
More specifically, to transfer wafers from the cassette to the wafer boat, load/unload means for loading and unloading wafers therebetween is moved first to a first position in which wafers can be carried out of the cassette, thereby carrying a single wafer out of the cassette, and then to a second position in which wafers can be carried into the wafer boat, thereby loading the single wafer into the wafer boat by the load/unload means.
Since in this treatment apparatus, the load/unload means is moved between the first and second positions each time it transfers a single wafer, a great amount of time is required to transfer a plurality of wafers from the cassette to the wafer boat, which is the major cause of hindrance to increase the throughput of the treatment apparatus. Accordingly, a long time is required to completely transfer all wafers contained in the cassette, and therefore it is necessary to keep the cassette for a long time in a position in which the wafers can be carried out by means of the load/unload means.